Boeing 747-8F Vomit Comet

A note on this page. The original clip used a Flash player that no longer works. It has been replaced with footage of the same event.

A 747-8 Freighter flies parabolic manoeuvres during the flight test programme — pushing over into near-weightlessness and back.

This is a certification test, not a stunt

The nickname comes from NASA’s reduced-gravity aircraft, but the reason a manufacturer flies parabolas is specific and unglamorous: fuel and oil systems have to keep working when gravity stops helping them.

Under normal flight the fuel in a 747’s wing tanks sits on the bottom of the tank, where the pumps are. In a pushover at low or negative g it does not. The aircraft has to demonstrate that:

• fuel keeps feeding all four engines through the manoeuvre and afterwards;
• engine oil and lubrication systems continue to function;
• nothing unports, cavitates or surges in a way that could cause a flameout.

The same test regime covers the other end of the envelope — sustained high-g manoeuvring loads — and sits alongside the extreme testing and the rejected takeoff test in the certification programme.

The 747-8’s wing was entirely new, with different fuel capacity and a different internal layout to the 747-400’s, so none of this could be inherited. It all had to be flown again.

Related

• Extreme testing of the 747-8
• The rejected takeoff test
• The 747-8 Freighter